|author||Hugh Dickins <email@example.com>||2014-02-06 15:56:01 -0800|
|committer||Tejun Heo <firstname.lastname@example.org>||2014-02-07 10:21:12 -0500|
cgroup: use an ordered workqueue for cgroup destruction
Sometimes the cleanup after memcg hierarchy testing gets stuck in mem_cgroup_reparent_charges(), unable to bring non-kmem usage down to 0. There may turn out to be several causes, but a major cause is this: the workitem to offline parent can get run before workitem to offline child; parent's mem_cgroup_reparent_charges() circles around waiting for the child's pages to be reparented to its lrus, but it's holding cgroup_mutex which prevents the child from reaching its mem_cgroup_reparent_charges(). Just use an ordered workqueue for cgroup_destroy_wq. tj: Committing as the temporary fix until the reverse dependency can be removed from memcg. Comment updated accordingly. Fixes: e5fca243abae ("cgroup: use a dedicated workqueue for cgroup destruction") Suggested-by: Filipe Brandenburger <email@example.com> Signed-off-by: Hugh Dickins <firstname.lastname@example.org> Cc: email@example.com # 3.10+ Signed-off-by: Tejun Heo <firstname.lastname@example.org>
Diffstat (limited to 'kernel')
1 files changed, 6 insertions, 2 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index e2f46ba37f7..aa95591c143 100644
@@ -4845,12 +4845,16 @@ static int __init cgroup_wq_init(void)
* There isn't much point in executing destruction path in
* parallel. Good chunk is serialized with cgroup_mutex anyway.
- * Use 1 for @max_active.
+ * XXX: Must be ordered to make sure parent is offlined after
+ * children. The ordering requirement is for memcg where a
+ * parent's offline may wait for a child's leading to deadlock. In
+ * the long term, this should be fixed from memcg side.
* We would prefer to do this in cgroup_init() above, but that
* is called before init_workqueues(): so leave this until after.
- cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1);
+ cgroup_destroy_wq = alloc_ordered_workqueue("cgroup_destroy", 0);